Mineral insulated (MI) cables generally include one or more conductors surrounded by mineral insulation, such as magnesium oxide powder, which is tightly packed inside a conductive, typically copper or steel, tubular sheath. With this construction, MI cables are compact, fire-resistant, and protected from electromagnetic interference. As such, MI cables are often used in applications where high power output, high exposure temperatures, or extreme resistance to environmental corrosives are needed. For example, these cables are often used in wiring systems where enhanced fire protection of electrical connections is necessary, such as fire and smoke alarm systems. These cables are also useful in enclosed areas, such as electrical or lighting systems for tunnel, subway, underground railway, or underground roadway applications.
Lengths of MI cable may be joined together using splice kits (or splices), for example, in cases where a cable's manufactured length is shorter than the run length or part of a cable is damaged and needs repair or replacement. To splice two MI cables together, each cable end is terminated by first stripping away the sheath and exposing the insulation and the conductors. The exposed insulation is then covered by one or more materials for protection against outside substances, moisture, and/or heat. Once the two MI cables are terminated, the exposed conductors of each cable are physically and electrically coupled together. To be fire-rated under the requirements of UL 2196, and thus usable in systems where enhanced fire protection is necessary, a splice kit must protect the internal cable conductors enough to permit circuit operation at increasing temperatures up to 1700 degrees Fahrenheit after one hour (for a one-hour rating) or up to 1850 degrees Fahrenheit after two hours (for a two-hour rating). The splice kit must also withstand mechanical impact resulting from water hose exposure.
Currently, factory-installed and field-installed fire-rated splice kits exist for joining two MI cables together (that is, two-way splicing). However, no kits or systems exist that provide fire-rated three-way splicing or T-splicing; users may attempt to patch together unlisted products with their own construction methods, but such patchwork installations cannot be listed as fire-rated systems under the above fire-listing requirements.
Therefore, what is needed is an integrated solution for a fire-rated three-way splice.